Temperature controlled loadlock chamber

ABSTRACT

A temperature controlled loadlock chamber for use in semiconductor processing is provided. The temperature controlled loadlock chamber may include one or more of an adjustable fluid pump, mass flow controller, one or more temperature sensors, and a controller. The adjustable fluid pump provides fluid having a predetermined temperature to a temperature-controlled plate. The mass flow controller provides gas flow into the chamber that may also aid in maintaining a desired temperature. Additionally, one or more temperature sensors may be combined with the adjustable fluid pump and/or the mass flow controller to provide feedback and to provide a greater control over the temperature. A controller may be added to control the adjustable fluid pump and the mass flow controller based upon temperature readings from the one or more temperature sensors.

TECHNICAL FIELD

This invention relates generally to the fabrication of semiconductor devices and, more particularly, to a method and structure to control the temperature of a wafer in a loadlock.

BACKGROUND

As integrated circuit feature sizes decrease, the gate dielectric thickness of field effect transistors (FETs) also decreases. This decrease is driven in part by the demands of overall device scaling. As gate conductor widths decrease, for example, other device dimensions decrease to maintain the proper device scale, and thus device operation. Another factor driving gate dielectric thickness reduction is the increased transistor drain current realized from a reduced gate dielectric thickness. The transistor drain current is proportional to the amount of charge induced in the transistor channel region by the voltage applied to the gate conductor. The amount of charge induced by a given voltage drop across the dielectric is a factor of the capacitance of the gate dielectric.

In order to achieve increased capacitance, gate dielectrics made from oxides such as SiO_(x) are now as thin as 10 Å. These extremely thin gate oxides result in increased gate-to-channel leakage current, however. Problems such as this have led to the use of materials that have dielectric constants that are greater than the dielectric constant of silicon oxide, which has a k value of about 3.9. Higher k values, for example 20 or more, may be obtained with various transition metal oxides, such as an oxynitride film. These high-k materials allow high capacitances to be achieved with relatively thick dielectric layers. In this manner, the reliability problems associated with very thin dielectric layers can be avoided while improving transistor performance.

There are, however, fabrication problems associated with forming gate dielectric layers that include high-k materials. Generally, semiconductor fabrication utilizes one or more cluster tools, which comprises various process chambers that can be utilized in association with a wafer handling system or device to perform a variety of semiconductor processes. These processes can include, for example, oxidation, nitridation, annealing, deposition processes, and the like.

In the example of forming a gate dielectric comprising an oxynitride film, a cluster tool may be used to perform an oxidation process, a nitridation process, and an anneal process, wherein each process is typically performed in different process chambers. Between chambers, a wafer is transferred through a loadlock chamber. The loadlock chamber typically has a non-adjustable cooling plate maintained at a specific temperature to cool the wafer. The oxidation chamber, however, fails to maintain a uniform temperature across the wafer. It has been found that this variation in the temperature across the wafer may result in a variation in the equivalent oxide thickness (EOT), which in turn results in a variation of the Idsat between FETs. This variation may be observed not only with FETs on different wafers, but also between FETs on different dies on a single wafer and between FETs on a single die. The variation in the Idsat may adversely affect the circuitry and reduce yield, thereby increasing costs.

Accordingly, there is a need for a method and a structure to maintain a more uniform temperature over a wafer during processing.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, and technical advantages are generally achieved by preferred embodiments of the present invention that provide a method and structure to maintain a more uniform temperature across a wafer during processing.

An embodiment of the invention provides a loadlock chamber for semiconductor processing. The loadlock includes a chamber, a temperature-controlled plate within the chamber and a chiller. The temperature-controlled plate has a first intake port and a first output port interconnected by tubing. The chiller has a second output port coupled to the first intake port and a second intake port coupled to the first output port. The chiller has an adjustable temperature for which the chiller may provide cooling fluid to the temperature-controlled plate via the second output port and the first intake port.

In another embodiment of the present invention, another loadlock chamber for semiconductor processing is provided. The loadlock chamber includes a chamber, a temperature-controlled plate within the chamber, an adjustable chiller, and a mass flow controller. The adjustable chiller is coupled to the temperature-controlled plate. The mass flow controller is coupled to a gas intake port in the chamber and allows a flow of gas into the chamber.

In another embodiment of the present invention, another loadlock chamber for semiconductor processing is provided. The loadlock chamber includes a chamber, a mass flow controller, a cooling plate, an adjustable chiller, one or more temperature sensors, and a controller. The cooling plate is located in an interior region of the chamber and is coupled to the chiller to allow the chiller to flow fluid at an adjustable temperature through the cooling plate. The controller is communicatively coupled to the one or more temperature sensors, the adjustable chiller, and the mass flow controller. The controller receives temperature readings from the one or more temperature sensors and adjusts one or both of the flow of gas through the mass flow controller and a temperature of the fluid flowing through the adjustable chiller.

Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the specific embodiments disclosed might be readily utilized as a basis for modifying or designing other structures or processes for carrying out the purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions and variations on the example embodiments described do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic of a loadlock chamber in accordance with an embodiment of the present invention;

FIG. 2 is a block diagram of a loadlock chamber in accordance with an embodiment of the present invention; and

FIG. 3 is a flow chart illustrating a process of controlling the temperature of a wafer in a loadlock chamber in accordance with an embodiment of the present invention.

Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale. To more clearly illustrate certain embodiments, a letter indicating variations of the same structure, material, or process step may follow a figure number.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The operation and fabrication of the presently preferred embodiments are discussed in detail below. However, the embodiments and examples described herein are not the only applications or uses contemplated for the invention. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention or the appended claims.

Exemplary structures and methods are provided below for fabricating a metal oxide semiconductor field effect transistor (MOSFET) according to embodiments of the invention. Although the exemplary embodiments are described as a series of steps, it will be appreciated that this is for illustration and not for the purpose of limitation. For example, some steps may occur in a different order than illustrated yet remain within the scope of the invention. In addition, not all illustrated steps may be required to implement the present invention. Furthermore, the structures and methods according to embodiments of the invention may be implemented in association with the fabrication or processing of other semiconductor structures not illustrated.

FIG. 1 schematically illustrates a cluster tool 100 in accordance with an embodiment of the present invention. The cluster tool 100 includes a first process chamber 112, a second process chamber 114, and a third process chamber 116 interconnected via a buffer chamber 120. In an embodiment, the first process chamber 112 is configured as an oxidation chamber, the second process chamber 114 is configured as a nitridation chamber, and the third process chamber 116 is configured as an annealing chamber, such as an RTA chamber, which preferably has an oxidizing ambient such as oxygen. Interconnected to the buffer chamber 120 are one or more loadlock chambers 121. The buffer chamber 120 and the one or more loadlock chambers 121 permit transferring one or more wafers between the first process chamber 112, the second process chamber 114, and the third process chamber 116 without breaking vacuum between processes or chambers.

The cluster tool 100 may optionally further include a front-opening unified pod (FOUP) docking system 122 and a factory interface 124. The FOUP docking system 122 and the factory interface 124 allow wafers to be loaded and unloaded without exposing the loadlock chambers 121, the buffer chamber 120, the first process chamber 112, the second process chamber 114, and the third process chamber 116 to air. The pressure of the FOUP docking system 122 is usually at about 1 atm (same as the fab environment), whereas that of a loadlock chamber 121 is much lower, typically under vacuum, e.g., less than about 10 Torr.

In operation, wafers are transferred into and out of the cluster tool 100, either individually or in batches, via the FOUP docking system 122. The wafers are transferred from the FOUP docking system 122 to the loadlock chamber 121 via the factory interface 124. Once transferred into the loadlock chambers 121, the wafers are isolated from the ambient environment. Typically, an inert gas such as nitrogen is purged through the loadlock chamber 121, which is pumped down to a low pressure, if not vacuum, typically ranging from 200 to 1000 Pa, to remove any air from the atmosphere. The wafers are transferred to one or more of the first process chamber 112, the second process chamber 114, and the third process chamber 116, which are also pumped down to a similar pressure to be in equilibrium with the pressure of the loadlock chambers 121, via the buffer chamber 120.

Processing may begin by one or more wafers being transferred from one or more of the loadlock chambers 121 into a processing chamber, e.g., the first process chamber 112, the second process chamber 114, and the third process chamber 116, using a belt, robotic arm, or other well-known transfer mechanism (not shown). Each of the processing chambers may be equipped with heating elements, gas flow orifices, radio frequency coils, and other equipment (not shown) necessary to affect the desired process.

In the illustrative embodiment, an oxide layer is deposited in the first process chamber 112. After formation of an oxide layer, the wafer is transferred from the first process chamber 112, via loadlock chambers 121, to the second process chamber 114. Thermal or plasma nitridation is performed in the second process chamber 114. Note that by utilizing cluster tool 100, vacuum need not be broken when transferring the wafer between processing chambers. This eliminates the possibility of the reactions of wafers with air or the moisture in the air. This also reduces the possibility of damage to the wafer from handling and the likelihood of contamination arising from exposure to the ambient environment. After nitridation, the wafer is transferred from the second process chamber 114, via the loadlock chambers 121, again without breaking vacuum, to the third process chamber 116 where the wafer is annealed.

It should be noted that FIG. 1 illustrates cluster tool 100 having three process chambers for illustrative purposes only. Other embodiments may include fewer or more process chambers. Additionally, other embodiments may utilize some, all, or none of the process chambers given above as examples. Embodiments of the present invention may be utilized, for example, in any cluster tool or other processing equipment wherein it is desirable to control the temperature of a wafer as it is being transported from a first location to a second location.

FIG. 2 illustrates a cross section view of a loadlock chamber 200, which may be used as one or more of the loadlock chambers 121 of FIG. 1, in accordance with an embodiment of the present invention. One of ordinary skill in the art will realize that FIG. 2 schematically illustrates an embodiment of the present invention and an actual embodiment of the invention may take any shape or form.

Generally, the loadlock chamber 200 comprises an enclosed chamber 210 having a top 212, a bottom 214, and sidewalls 216. Holders 218 are positioned to hold one or more wafers during transport. A temperature-controlled plate 220 is positioned along the bottom 214 and is coupled to an adjustable chiller 222. The chiller 222 provides cooling water via a chiller output port 248 to the temperature-controlled plate 220 via a temperature-controlled plate input port 244, and the cooling water is returned from the temperature-controlled plate 220 via a temperature-controlled plate output port 246 to the chiller 222 via a chiller input port 250. In an embodiment, the chiller 222 is adjustable to supply a cooling liquid, such as water, having an adjustable temperature to the temperature-controlled plate 220. The chiller 222 may also be adjusted to provide the cooling liquid at an adjustable pressure. Generally, the temperature-controlled plate 220 includes tubing made of a material having good thermal conductivity properties. In an embodiment, copper tubing is used and the chiller 222 is adjustable to provide the cooling liquid having a temperature from about 17° C. to about 120° C., but more preferably from about 30° C. to about 90° C. Additionally, it is preferred that the chiller 222 and the temperature-controlled plate 220 are a pressurized system having a pressure ranging from about 1 atm to about 10 atm.

The temperature-controlled plate 220 may also include raised portions, such as a plurality of pins 223 upon which a wafer may rest. The height of the plurality of pins 223 may be adjusted to maximize the cooling effect, including the rate of cooling, needed for a particular application. For example, it has been found that the height of the pins may be reduced to shorten the period of time required to cool the wafer to a specific temperature. In an embodiment, the height of the plurality of pins 223 is between about 1 mm and about 0.1 mm. Other heights, however, may be used. It should also be noted that other shapes may be used. For example, the pins may be any shape and may comprise ridges or a spiral shape on the temperature-controlled plate 220.

FIG. 2 also illustrates a mass flow controller 230 and a control valve 232 in accordance with an embodiment of the present invention. The mass flow controller 230 and the control valve 232 act together to create and maintain a gas atmosphere within the loadlock chamber 200. In particular, the mass flow controller 230 is coupled to a source gas 234 to control the flow of gas into the loadlock chamber 200, and the control valve 232 is coupled to the loadlock chamber 200 to release gas from within the loadlock chamber 200 by pump. In an embodiment, the mass flow controller 230 and the control valve 232 cooperate to maintain a specific pressure within the loadlock chamber 200. Preferably, the mass flow controller 230 and the control valve 232 are configured to maintain an atmospheric pressure within the loadlock chamber 200 from about 3 Torr to about 760 Torr.

In a preferred embodiment, the loadlock chamber 200 includes a temperature sensor 240, such as an infra-red temperature sensor, communicatively coupled to a controller 242, which may also be communicatively coupled to the chiller 222, the mass flow controller 230, and/or the control valve 232. In this embodiment, the controller 242 receives temperature information from the temperature sensor 240 and automatically controls the chiller 222, the mass flow controller 230, and/or the control valve 232 to maintain a desired temperature. The desired temperature may be based upon, among other things, the previous process, the subsequent process, the wafer size and thickness, and the like.

It should also be noted that FIG. 2 illustrates a single temperature sensor 240 for illustrative purposes only. It may be desirable in some embodiments of the present invention to utilize multiple temperature sensors, and possibly different types of temperature sensors. For example, multiple temperature sensors may be positioned in various locations within the loadlock chamber 200 to provide temperature measurements in various regions of the wafer. The locations may include, for example, various locations across the wafer as well as both sides of the wafer.

FIG. 3 is a flow diagram illustrating a procedure that may be performed to control the temperature of a wafer in accordance with an embodiment of the present invention. The process begins in step 305, wherein a desired temperature is set. The desired temperature may be set by a user, read from a database, or the like. It should be noted that the desired temperature may be based upon the process or processes being performed on the wafer. For example, the desired temperature may be set to a first temperature immediately after a first process has been performed to cause the temperature of the wafer to decrease slowly or quickly, or to cause the temperature of the wafer to increase slowly or quickly. A second process may require different temperatures. As another example, it may be desirable to maintain a specific wafer temperature prior to performing a specific process.

The process then proceeds to step 310, wherein one or more temperature samples are received. The temperature samples may be received from a single temperature sensor or from multiple temperature sensors placed in different locations within the loadlock chamber 200. For example, temperature sensors may be placed across the top surface 212 of the loadlock chamber 200 spaced apart such that the temperature sensors measure different portions of the wafer, including around the perimeter and the interior of the wafer. Additional temperature sensors may be placed to measure the temperature along the bottom of the wafer.

In step 312, a determination is made whether or not the temperature needs adjusting. The desired temperature (see step 305) is compared to the temperature samples and an adjustment, if necessary, is determined. If a determination is made that an adjustment is necessary, then processing proceeds to step 314, wherein an adjustment is made. The adjustment may include, for example, increasing the gas flow and pressure via the mass flow controller 230, reducing the gas flow and pressure via the mass flow controller 230 and the control valve 232, adjusting the temperature of the cooling fluid supplied by the chiller 222, adjusting the flow rate of the cooling fluid supplied by the chiller 222, and/or the like.

If in step 312 a determination is made that an adjustment is not necessary, then processing returns to step 310, wherein new temperature samples are received for processing.

It should be noted that the embodiment of the present invention discussed above assumes that the loadlock chamber 200 be equipped with both an adjustable chiller and a mass flow controller for providing temperature adjustment by fluid and gas, respectively. Embodiments of the present invention, however, may utilize one or more of these features. For example, an embodiment of the present invention may utilize an adjustable chiller, another embodiment of the present invention may utilize an adjustable chiller with a temperature sensor, another embodiment of the present invention may utilize a mass flow controller to maintain a specific temperature, another embodiment of the present invention may utilize a mass flow controller with a temperature sensor, and another embodiment may utilize an adjustable chiller, a mass flow controller, and a temperature sensor.

One of ordinary skill in the art will realize that the temperature controlled loadlock chamber disclosed herein provides dynamic controls and a feedback loop for maintaining optimum temperatures for a specific process. In this manner, more uniform semiconductor devices, including more uniform gate dielectrics, may be created. The increased uniformity will enable more accurate and uniform circuits to be created.

Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, it will be readily understood by those skilled in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present invention. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

What is claimed is:
 1. A loadlock assembly for semiconductor processing, the loadlock assembly comprising: a loadlock chamber having sidewalls, a top, a bottom, and a plurality of openings through which access may be gained to the loadlock chamber; a temperature-controlled plate within the loadlock chamber, the temperature-controlled plate having a first intake port and a first output port; a chiller having a second output port coupled to the first intake port and a second intake port coupled to the first output port, the chiller having an adjustable temperature within a range of temperatures at which the chiller may provide cooling fluid to the temperature-controlled plate via the second output port and the first intake port; a mass flow controller configured to provide gas to an interior region of the loadlock chamber; one or more temperature sensors on a at least one of the sidewalls, the top, or the bottom of the loadlock chamber and within and exposed to the interior region of the loadlock chamber, the one or more temperature sensors being above the temperature-controlled plate, the one or more temperature sensors being configured to measure a temperature of a wafer on the temperature-controlled plate as one or more temperature samples; and a controller communicatively coupled to the one or more temperature sensors and to the chiller, the controller being configured to adjust the adjustable temperature based at least in part on the one or more temperature samples of the wafer received from the one or more temperature sensors, wherein the controller is configured to adjust a flow rate of the gas supplied by the mass flow controller based at least in part on the one or more temperature samples of the wafer received from the one or more temperature sensors.
 2. The loadlock assembly of claim 1, wherein the temperature-controlled plate includes a plurality of pins.
 3. The loadlock assembly of claim 1, wherein the chiller provides cooling liquid at a pressure of about 1 atm to about 10 atm.
 4. The loadlock assembly of claim 1, wherein the range of temperatures is about 17° C. to about 120° C.
 5. A loadlock assembly for semiconductor processing, the loadlock assembly comprising: a loadlock chamber having sidewalls, a top, and a bottom, the loadlock chamber being separable from any process chambers; a temperature-controlled plate within the loadlock chamber; one or more temperature sensors mounted on at least one of the sidewalls, the top, or the bottom and within the loadlock chamber, the one or more temperature sensors being above the temperature-controlled plate and being configured to measure a temperature of a wafer on the temperature-controlled plate as one or more temperature samples; an adjustable chiller coupled to the temperature-controlled plate, the adjustable chiller configured to provide cooling liquid to the temperature-controlled plate; a gas intake port in the loadlock chamber; a mass flow controller coupled to the gas intake port, the mass flow controller configured to allow a flow of gas into the loadlock chamber; and a controller communicatively coupled to the one or more temperature sensors, the adjustable chiller, and the mass flow controller, the controller configured to receive one or more temperature samples of the wafer from the one or more temperature sensors and to adjust both the mass flow controller and the adjustable chiller based upon the one or more temperature samples of the wafer.
 6. The loadlock assembly of claim 5, wherein the adjustable chiller is configured to provide cooling liquid at a pressure of about 1 atm to about 10 atm.
 7. The loadlock assembly of claim 5, wherein the adjustable chiller is configured to provide cooling liquid at any temperature between about 17° C. and about 120° C.
 8. The loadlock assembly of claim 5, wherein the controller is configured to control at least one of a temperature or a pressure of the cooling liquid provided by the adjustable chiller to the temperature-controlled plate based at least in part on the one or more temperature sensors.
 9. The loadlock assembly of claim 5, wherein the controller is configured to control a flow rate of gas into the loadlock chamber by the mass flow controller based at least in part on the one or more temperature sensors.
 10. A loadlock assembly for semiconductor processing, the loadlock assembly comprising: a loadlock chamber having an interior region and an exterior region, the loadlock chamber having a first port, wherein the loadlock chamber is divisible from processing chambers; a mass flow controller coupled to the loadlock chamber, the mass flow controller is configured to provide gas to the interior region of the loadlock chamber; a cooling plate in the interior region of the loadlock chamber; an adjustable chiller coupled to the cooling plate, the adjustable chiller being configured to flow fluid at an adjustable temperature through the cooling plate; one or more temperature sensors in the interior region and on an interior wall of the loadlock chamber, the one or more temperature sensors being above the cooling plate and being configured to measure a temperature of a wafer on the cooling plate as one or more temperature samples; and a controller communicatively coupled to the one or more temperature sensors, the adjustable chiller, and the mass flow controller, the controller configured to receive the one or more temperature samples of the wafer from the one or more temperature sensors and to adjust both the mass flow controller and the adjustable chiller based upon the one or more temperature samples of the wafer.
 11. The loadlock assembly of claim 10, wherein the gas comprises nitrogen or helium.
 12. The loadlock assembly of claim 10, wherein the adjustable chiller provides cooling liquid at a pressure of about 1 atm to about 10 atm.
 13. The loadlock assembly of claim 10, wherein the adjustable chiller is configured to provide cooling liquid at any temperature between about 17° C. and about 120° C.
 14. The loadlock assembly of claim 10, wherein the controller is configured to adjust the temperature of the fluid at which the adjustable chiller provides cooling liquid to the cooling plate.
 15. The loadlock assembly of claim 10, wherein the controller is configured to adjust a flow rate of gas supplied by the mass flow controller. 